1) Field of the Invention
The present invention is directed to acoustic sensors as bionic cochlea.
2) Description of Prior Art
The most widely used prosthetic hearing device for deaf persons is the Cochlear implant (CI). The CI is an electronic device that uses conventional electronics and microphones to generate electrical signals that are fed into the damaged cochlea. The CI uses a stimulator implanted under the skin in combination with a battery powered microphone and processing electronics located outside the body. The two are attached together by a magnet. Sound waves detected by the external CI system are converted into electrical signals transmitted across the skin to the inner stimulator. The inner stimulator feeds electric signals inside the cochlea. Cochlear implants provide limited hearing to patients. The quality of sound is significantly different from a normal cochlea with less sound information being received and processed by the brain. Cochlear implants differ from hearing aids because they feed electrical signals to the auditory nerve inside the cochlea rather than amplifying sound and feeding the amplified sound to the ear drum.
In general, acoustics sensors use some type of transducer or microphone to sense acoustic energy, e.g., voice, music and vibrations. Air and contact, e.g., bone conduction, microphone elements utilize piezoelectric materials such as ceramic disk or polyvinylidene fluoride (PVDF) films. In a ceramic disk microphone, the ceramic disk is generally round and is glued to a thin metal substrate such as brass. The center of the disc is positive while the brass substrate is negative. In a PVDF film microphone, the PVDF film is either mounted to a metal, plastic or polymer substrate or is stretched over the open end of a cylinder so the film can vibrate freely.
Air microphones do not work well in high-noise environments as they pick up ambient noise along with any acoustic signals of interest. Bone conduction microphones are used in communication systems for the transmission of speech. When a person speaks, the cranial bones vibrate in accordance with the sounds that are produced by the vocal cords. Bone conduction microphones detect vibrations in the cranial bones and convert these vibrations to electrical signals that are fed into a two way radio. Bone conduction microphones are very useful in high-noise environments, but must firmly press against the bones in the skull in order to consistently detect vibrations. Over time, a bone conduction microphone becomes uncomfortable because of the constant pressure on a person's head.
Therefore, an acoustic sensor is desired that can be used as a bionic cochlea and that overcomes the poor sound quality of a CI and that avoids the problems with current air and contact microphones.